Radial coverage piston ring groove arrangement

ABSTRACT

A piston ring may comprise a first face configured to form a first seal between the piston ring and a cylindrical ID bore, a second face configured to form a second seal between the piston ring and a carbon seal assembly, and a third face configured to interface with a surface of a spring, wherein the third face is longer than the surface of the spring.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of, and claims priority to, and thebenefit of U.S. patent application Ser. No. 14/600,858, filed on Jan.20, 2015, and entitled “RADIAL COVERAGE PISTON RING GROOVE ARRANGEMENT”which is incorporated by reference herein in its entirety.

FIELD

The present disclosure relates to seals and more particularly to mainshaft bearing compartment seals.

BACKGROUND

A conventional main shaft bearing compartment seal system 100 isdepicted in FIG. 1B. Notably, system 100 includes a traditional pistonring and wave spring within a groove assembly. In response to radialeccentricity of each part in the opposite respective radial directions,the radial coverage is low between a piston ring face and a wave springface. Having low values of face coverage may cause wave springdistortion. This could negatively impact the function and performance ofthe seal assembly and engine.

SUMMARY

According to various embodiments, a main shaft bearing compartment sealsystem is described herein. The system may include a cylindrical IDbore. The system may include a carbon seal assembly juxtaposedsubstantially adjacent to a portion of the cylindrical ID bore. Thecarbon seal assembly may comprise a first step and a second step. Thesystem may include a piston ring, wherein the piston ring is cylindricaland substantially surrounds the cylindrical ID bore. The system mayinclude a spring configured to interface with a surface of the pistonring. Dimensions of the piston ring may provide physical fool proofing.The spring may be a wave spring. A piston ring face configured tointerface with spring face may be longer than the spring face.

A width of the second step may be sized to prevent the spring fromentering a gap formed between the piston ring and the carbon sealassembly. According to various embodiments, in response to the carbonseal assembly bottom contacting at one circumferential location, theinterface between a piston ring face and a spring face may be maintainedto acceptable levels, for instance the interface between the piston ringface and the spring face may be no less than 66% coverage. Dimensions ofthe first step of the carbon seal assembly provide physical foolproofing.

According to various embodiments, a carbon seal assembly is disclosedherein. The carbon seal assembly may include a first step; and a secondstep or a first groove and a second groove. The carbon seal assembly maybe juxtaposed substantially adjacent to a portion of a cylindrical IDbore. A piston ring may be configured to interface with a face of thecarbon seal assembly. The piston ring may be cylindrical andsubstantially surrounds the cylindrical ID bore, and wherein a springmay be configured to interface with a surface of the piston ring.

According to various embodiments, a piston ring is described herein. Thepiston ring may include a first face configured to form a first sealbetween the piston ring and a cylindrical ID bore. The piston ring mayinclude a second face configured to form a second seal between thepiston ring and a carbon seal assembly. The piston ring may include athird face configured to interface with a surface of a spring. The thirdface may be longer than the surface of the spring.

The forgoing features and elements may be combined in variouscombinations without exclusivity, unless expressly indicated hereinotherwise. These features and elements as well as the operation of thedisclosed embodiments will become more apparent in light of thefollowing description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the present disclosure is particularly pointed outand distinctly claimed in the concluding portion of the specification. Amore complete understanding of the present disclosure, however, may bestbe obtained by referring to the detailed description and claims whenconsidered in connection with the drawing figures, wherein like numeralsdenote like elements.

FIG. 1A is a cross-sectional view of a gas turbine engine, in accordancewith various embodiments;

FIG. 1B depicts a conventional main shaft bearing compartment sealsystem;

FIGS. 2A-2D depict isometric and isometric cut-away views of an improvedradial coverage piston ring groove arrangement in accordance withvarious embodiments;

FIG. 2E depicts a cross-sectional cut-away side view of an improvedradial coverage piston ring groove arrangement in accordance withvarious embodiments; and

FIG. 3 depicts an improved radial coverage piston ring groovearrangement with a non-centered carbon seal assembly in accordance withvarious embodiments.

DETAILED DESCRIPTION

The detailed description of exemplary embodiments herein makes referenceto the accompanying drawings, which show exemplary embodiments by way ofillustration. While these exemplary embodiments are described insufficient detail to enable those skilled in the art to practice theinventions, it should be understood that other embodiments may berealized and that logical, chemical and mechanical changes may be madewithout departing from the spirit and scope of the inventions. Thus, thedetailed description herein is presented for purposes of illustrationonly and not of limitation. For example, the steps recited in any of themethod or process descriptions may be executed in any order and are notnecessarily limited to the order presented. Furthermore, any referenceto singular includes plural embodiments, and any reference to more thanone component or step may include a singular embodiment or step. Also,any reference to attached, fixed, connected or the like may includepermanent, removable, temporary, partial, full and/or any other possibleattachment option. Additionally, any reference to without contact (orsimilar phrases) may also include reduced contact or minimal contact.

Different cross-hatching and/or surface shading may be used throughoutthe figures to denote different parts but not necessarily to denote thesame or different materials.

FIG. 1A schematically illustrates an example gas turbine engine 20 thatincludes a fan section 22, a compressor section 24, a combustor section26 and a turbine section 28. Alternative engines might include anaugmenter section (not shown) among other systems or features. The fansection 22 drives air along a bypass flow path B while the compressorsection 24 draws air in along a core flow path C where air is compressedand communicated to a combustor section 26. In the combustor section 26,air is mixed with fuel and ignited to generate a high pressure exhaustgas stream that expands through the turbine section 28 where energy isextracted and utilized to drive the fan section 22 and the compressorsection 24.

Although the disclosed non-limiting embodiment depicts a turbofan gasturbine engine, it should be understood that the concepts describedherein are not limited to use with turbofans as the teachings may beapplied to other types of turbine engines; for example a turbine engineincluding a three-spool architecture in which three spoolsconcentrically rotate about a common axis and where a low spool enablesa low pressure turbine to drive a fan via a gearbox, an intermediatespool that enables an intermediate pressure turbine to drive a firstcompressor of the compressor section, and a high spool that enables ahigh pressure turbine to drive a high pressure compressor of thecompressor section.

The example gas turbine engine 20 generally includes a low speed spool30 and a high speed spool 32 mounted for rotation about an enginecentral longitudinal axis X relative to an engine static structure 36via various bearing systems 38. It should be understood that variousbearing systems 38 at various locations may alternatively oradditionally be provided.

The low speed spool 30 generally includes an inner shaft 40 thatconnects a fan 42 and a low pressure (or first) compressor 44 section toa low pressure (or first) turbine 46 section. The inner shaft 40 drivesthe fan 42 through a speed change device, such as a geared architecture48, to drive the fan 42 at a lower speed than the low speed spool 30.The high speed spool 32 includes an outer shaft 50 that interconnects ahigh pressure (or second) compressor 52 section and a high pressure (orsecond) turbine section 54. The inner shaft 40 and the outer shaft 50are concentric and rotate via the various bearing systems 38 about theengine central longitudinal axis X.

A combustor 56 is arranged between the high pressure compressor 52 andthe high pressure turbine 54. In one example, the high pressure turbine54 includes at least two stages to provide a double stage high pressureturbine 54. In another example, the high pressure turbine 54 includesonly a single stage. As used herein, a “high pressure” compressor orturbine experiences a higher pressure than a corresponding “lowpressure” compressor or turbine.

The example low pressure turbine 46 has a pressure ratio that is greaterthan about 5. The pressure ratio of the example low pressure turbine 46is measured prior to an inlet of the low pressure turbine 46 as relatedto the pressure measured at the outlet of the low pressure turbine 46prior to an exhaust nozzle.

A mid-turbine frame 57 of the engine static structure 36 is arrangedgenerally between the high pressure turbine 54 and the low pressureturbine 46. The mid-turbine frame 57 further supports various bearingsystems 38 in the turbine section 28 as well as setting airflow enteringthe low pressure turbine 46.

The core airflow C is compressed by the low pressure compressor 44 thenby the high pressure compressor 52 mixed with fuel and ignited in thecombustor 56 to produce high speed exhaust gases that are then expandedthrough the high pressure turbine 54 and low pressure turbine 46. Themid-turbine frame 57 includes vanes 59, which are in the core airflowpath and function as an inlet guide vane for the low pressure turbine46. Utilizing the vane 59 of the mid-turbine frame 57 as the inlet guidevane for low pressure turbine 46 decreases the length of the lowpressure turbine 46 without increasing the axial length of themid-turbine frame 57. Reducing or eliminating the number of vanes in thelow pressure turbine 46 shortens the axial length of the turbine section28. Thus, the compactness of the gas turbine engine 20 is increased anda higher power density is achieved.

The disclosed gas turbine engine 20 in one example is a high-bypassgeared aircraft engine. In a further example, the gas turbine engine 20includes a bypass ratio greater than about six (6), with an exampleembodiment being greater than about ten (10). The example gearedarchitecture 48 is an epicyclical gear train, such as a planetary gearsystem, star gear system or other known gear system, with a gearreduction ratio of greater than about 2.3.

In one disclosed embodiment, the gas turbine engine 20 includes a bypassratio greater than about ten (10:1) and the fan diameter issignificantly larger than an outer diameter of the low pressurecompressor 44. It should be understood, however, that the aboveparameters are only exemplary of one embodiment of a gas turbine engineincluding a geared architecture and that the present disclosure isapplicable to other gas turbine engines.

With reference to Prior Art FIG. 1B a seal assembly, such as a carbonseal housing 110, piston ring 130, spring 140 and cylindrical ID bore120. A carbon seal housing 110 may comprise a carrier configured to holda piston ring 130. The piston ring 130 may be a torus, and/or a slottedtorus. The piston ring 130 may be configured to create seals. Forinstance, a fluid-tight seal may be created between a first surface 134of the piston ring 130 and a first surface 122 of the cylindrical IDbore 120. The piston ring 130 may be configured to seal air fromentering a bearing compartment. A fluid-tight seal may be createdbetween a second surface 136 of the piston ring 130 and a first surface112 of the carbon seal housing 110.

These components may reciprocate axially and/or experience vibration.These components may also experience radial eccentricity which mayinvolve components moving off-center. The size of gap B may increasebetween the carbon seal housing 110 and the cylindrical ID bore 120, atleast with respect with a portion of the carbon seal housing 110, inresponse with this radial eccentricity and/or vibration. The size of gapA is constant. As the size of gap B increases, spring 140 tends totravel in concert with the carbon seal housing 110. This leads to afirst face 142 of spring 140 being off-center with respect to a thirdface 132 of carbon seal housing 110. Having low values of face coveragemay cause wave spring distortion. This could negatively impact thefunction and performance of the seal assembly and associated engine.

According to various embodiments and with reference to FIGS. 2A-2E, aradial coverage piston ring groove arrangement seal assembly isdisclosed. The seal assembly may comprise a carbon seal housing 210, apiston ring 230, spring 240 and cylindrical ID bore 220. The carbon sealhousing 210 may comprise a carrier configured to hold a piston ring 230.The piston ring 230 may be a torus, and/or a slotted torus. The pistonring 230 may at least partially circumferentially wrap around acylindrical ID bore 220. The piston ring 230 may be configured to createseals. For instance, a fluid-tight seal may be created between a firstsurface 234 of the piston ring 230 and a first surface 222 of thecylindrical ID bore 220. The piston ring 230 may be configured to sealair from entering the bearing compartment. A fluid-tight seal may becreated between a second surface 236 of the piston ring 230 and a firstsurface 212 of the carbon seal housing 210. A portion of the carbon sealhousing 210 may circumferentially wrap around both the piston ring 230and a portion of the cylindrical ID bore 220. Piston ring 230 may bemade from any suitable material, such as cast iron, steel, anon-metallic material, carbon graphite and/or the like. Spring 240 maybe any spring configured to properly position piston ring 230 withincarbon seal housing 210. According to various embodiments, spring 240may be a wave spring. A wave spring (sometimes referred to as a coiledwave spring or a scrowave spring), is a generally flat cylindricalarticle of material, similar to a washer, to which waves are added toimpart a spring effect. The number of turns and waves can be adjusted toproduce a weaker or a stronger force.

According to various embodiments and reference to FIG. 2E, piston ring230 may be shaped such that its shape renders it difficult or impossibleto install in an incorrect orientation. For instance, first step 215 ofcarbon seal housing 210 may extend in such as manner as to physicallyinterfere with an OD (bottom) surface 213 of piston ring 230 shouldpiston ring 230 be attempted to be inserted within carbon seal housing210 backwards. Additionally, should spring 240 be attempted to beinserted contacting second surface 236 rather than third face 232,piston ring 230 will be physically restricted from insertion withincarbon seal housing 210 due to interference with first step 215 and/orsecond step 218. First step 215 may be defined by radial surface (alsoreferred to herein as a third radial surface) 215 a and axial surface(also referred to herein as a first axial surface) 215 b. Second step218 may be defined by radial surface (also referred to herein as afourth radial surface) 218 a and axial surface (also referred to hereinas a second axial surface) 218 b.

According to various embodiments, third face 232 of piston ring 230 maybe longer measured from the inner diameter to the outer diameter thatthe length of spring 240 measured from the inner diameter to the outerdiameter. For instance, third face 232 of piston ring 230 may be longerthan a first face 242 of spring 240. This may increase coverage andcontact between the piston ring 230 and the spring 240, particularly, inresponse to a scenario where the carbon seal housing 210 has bottomcontacted at one circumferential location (see FIG. 3 for an example ofthe carbon seal housing 210 has bottom contacted at one circumferentiallocation). Third face 232 of piston ring 230 is radially longer thanthird face 132 of piston ring 130. As illustrated in FIG. 2E, spring 240may be coupled between third face (also referred to herein as a pistonring face) 232 and radial surface (also referred to herein as a secondradial surface) 214 of carbon seal housing 210.

According to various embodiments, second step 218 of the carbon sealhousing 210 may be sized such that spring 240 is restricted fromentering gap C. Stated another way, a width of the second step is sizedto prevent the spring from entering a gap adjacent to the second stepformed between the piston ring and the carbon seal assembly. Forinstance, the width of second step 218 is greater than about half theheight of spring 240. Spring 240 is taller, axially, than spring 140(see axis X-X′).

According to various embodiments and with reference to FIG. 3, ascenario where the carbon seal housing 210 has bottom contacted at onecircumferential location is depicted. In this way, gap B′ is aboutdoubled as compared to gap B as shown in FIG. 2E and gap A is maintained(as a constant size) from its size in FIG. 2E. Spring 240 has traveledaway from cylindrical ID bore 220 with the carbon seal housing 210. Ahigh percentage of radial coverage between third face 232 of piston ring230 and first face of spring 240 may be maintained as compared withconventional methods. For instance, radial coverage between third face232 of piston ring 230 and first face of spring 240 is no less thanabout 66% coverage of first face 242 of spring 240.

A modified ring groove geometry that creates 2 distinct cavities orsteps 215, 218 for the piston ring 230 and spring 240 is describedherein. This concept provides a separate groove cavity for the spring240 (step 218), independent of the clearance cavity. This modified ringgroove geometry increases first face 242 coverage and reduces exposurerisk for eccentricity of spring 240 to piston ring 230, to avoidpotential disengagement and improve function and performance of the sealassembly and engine. These improvements are achieved while maintainingother design constraints such as resistance to incorrectinstallation/assembly and desired clearances.

Advanced, high-performance engines would benefit from improvedperformance main shaft bearing compartment seals while also meeting moreaggressive cost, weight, size and reliability metrics. Improvedcapability main shaft bearing compartment carbon seals tend to meet theincreased demands of next generation high-performance engines. Carbonseals enable the engine and bearing compartment to function with minimalimpact on Thrust Specific Fuel Consumption (TSFC), the ThermalManagement System (TMS) and the Lubrication System. Current and futureengine programs would benefit from seals with improved wear.

Benefits, other advantages, and solutions to problems have beendescribed herein with regard to specific embodiments. Furthermore, theconnecting lines shown in the various figures contained herein areintended to represent exemplary functional relationships and/or physicalcouplings between the various elements. It should be noted that manyalternative or additional functional relationships or physicalconnections may be present in a practical system. However, the benefits,advantages, solutions to problems, and any elements that may cause anybenefit, advantage, or solution to occur or become more pronounced arenot to be construed as critical, required, or essential features orelements of the inventions. The scope of the inventions is accordinglyto be limited by nothing other than the appended claims, in whichreference to an element in the singular is not intended to mean “one andonly one” unless explicitly so stated, but rather “one or more.”Moreover, where a phrase similar to “at least one of A, B, or C” is usedin the claims, it is intended that the phrase be interpreted to meanthat A alone may be present in an embodiment, B alone may be present inan embodiment, C alone may be present in an embodiment, or that anycombination of the elements A, B and C may be present in a singleembodiment; for example, A and B, A and C, B and C, or A and B and C.Systems, methods and apparatus are provided herein. In the detaileddescription herein, references to “one embodiment”, “an embodiment”,“various embodiments”, etc., indicate that the embodiment described mayinclude a particular feature, structure, or characteristic, but everyembodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed. After reading the description, it will be apparent to oneskilled in the relevant art(s) how to implement the disclosure inalternative embodiments.

Furthermore, no element, component, or method step in the presentdisclosure is intended to be dedicated to the public regardless ofwhether the element, component, or method step is explicitly recited inthe claims. No claim element herein is intended to invoke 35 U.S.C.112(f), unless the element is expressly recited using the phrase “meansfor.” As used herein, the terms “comprises”, “comprising”, or any othervariation thereof, are intended to cover a non-exclusive inclusion, suchthat a process, method, article, or apparatus that comprises a list ofelements does not include only those elements but may include otherelements not expressly listed or inherent to such process, method,article, or apparatus.

What is claimed is:
 1. A piston ring, comprising: a first faceconfigured to form a first seal between the piston ring and acylindrical ID bore; a second face configured to form a second sealbetween the piston ring and a carbon seal assembly; and a third faceconfigured to interface with a surface of a spring, wherein the thirdface is longer than the surface of the spring.
 2. The piston ring ofclaim 1, wherein the spring is a wave spring.
 3. The piston ring ofclaim 1, wherein the carbon seal assembly comprises a first step and asecond step.
 4. The piston ring of claim 3, wherein a width of thesecond step is sized to prevent a portion of the spring from entering agap formed between the piston ring and the carbon seal assembly.
 5. Thepiston ring of claim 3, wherein dimensions of the first step of thecarbon seal assembly provide resistance to improper installation.
 6. Thepiston ring of claim 1, wherein in response to the carbon seal assemblybottom contacting at one circumferential location, the interface betweena face of the piston ring and the spring is no less than about 66%coverage of contact between a face of the piston ring and the surface ofthe spring.